Take a minute and watch the video I have linked below. This is 3D flying. You use the engine and prop to fly the plane more than the wing for most of the manouvers. Control surfaces on planes designed for 3D flight tend to be larger as well as they rely hevely on the prop wash for control as aposed to airspeed flowing over them.

http://www.ohiomodelplanes.com/62kat...t70aerofun.wmv

An prop 11x4 would have more pulling power and spin up faster where an 11x7 would have a higher top speed but might take a little longer to get to it while the prop spins up depending on what engine you have it on. I have used an 11x7.5 on an OS .46 FX and an OS .50 SX and the diference is amazing. The 46 flys with it fine but the 50 uses it more efficiently. So for speed with my 50 I use an 11x7.5 and for 3D I use a 13x4.